This invention relates generally to an energy storage system, and more particularly to a method and apparatus for managing power sources in a vehicle.
At least some known vehicles, for example, railroad locomotives are equipped with systems for automatically starting and stopping their engines when one or more conditions exist. The primary purpose of such systems is to conserve fuel, thereby lowering fuel costs while also preserving precious energy resources. For instance, a locomotive may be configured to automatically shutdown after operating for a certain amount of time in a parked idle state to prevent the locomotive from needlessly wasting fuel. The locomotive may then automatically restart when, for example, an operator signals an intention to motor the locomotive, such as by moving a direction controller (known as a reverser) from a center position (that is, from a “neutral” position). A locomotive may also be configured to automatically restart a certain amount of time following an automatic shutdown, such as two or four hours, or when other conditions exist.
The automatic engine start and stop (AESS) system described above has been implemented not only in locomotives which operate independently, but also in multiple locomotives that operate together (i.e., in consist) for providing cumulative (or reserve) towing capacity. The front locomotive in the consist is usually designated the lead unit while the other locomotives are designated trail units. Each trail unit typically receives a trainline or radio signal representing the position of the lead unit's reverser, and treats that signal as representing the position of its own reverser (which is typically placed in the center position when configuring the locomotive for trail unit operation). In the case where a locomotive's reverser must be in the center position to enable the AESS system, placing the lead unit's reverser in the center position will allow the AESS system to be enabled in each locomotive in the consist. Similarly, in the case where moving an automatically shutdown locomotive's reverser from the center position induces an automatic engine restart, moving the reverser in an automatically shutdown lead unit from the center position induces an automatic restart for each automatically shutdown locomotive in the consist. To start the diesel engine, locomotives include an energy storage system that is utilized to start the diesel engine and to provide electrical power to various devices installed on the locomotive. During operation, an alternator driven by the diesel engine, continuously recharges the energy storage system to ensure that the energy storage system remains charged to a predetermined voltage level.
However, AESS in the locomotive is configured to stop the engine after the engine is idled for a predetermined time to save fuel. Shutting down the engine can occur several times a day and the amount of time available after each start may not allow battery to fully charge. AESS checks the battery voltage and battery current before shutting down the engine, however the charger measures charger voltage and charger current to determine if the engine can be shut down. However, charger current and charger voltage is not accurately indicative of the state of charge of the battery and the engine may be shut down even if the State of Charge (SOC) of the battery is very low. The shut down of engine at low SOC of battery results in a failure to crank the engine at the next restart and road failures.
During charging, the batteries on a locomotive are charged at a voltage based on ambient temperature. In some cases, there is a large difference between ambient temperature and the battery temperature due to long thermal constant of the batteries. The large difference between the battery temperature and the ambient temperature sensor reading provides inaccurate information to the charger causing the charger to charge the batteries at higher voltage than is actually required by the battery state of charge. Charging at this higher voltage results in undesirable gassing of the batteries.